Development of Efficient R-134a A/C System of a Medium Size Car

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1 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) Development of Efficient R-134a A/C System of a edium Size Car A.D. Desai* 1, S.N. Sapali #, and G.V. artasarati & Abstract Automotive air conditioning (A/C) system is constantly undergoing improvements over te past decades to acieve iger efficiency. Internal eat excanger (IX) so far, as not been given muc importance to use in car A/C systems. e IX transfers eat from te condenser outlet to te suction gas. Altoug previous researcers ave investigated performance of IX, tis study can be distinguised from te previous studies wit respect to te type, size and material used for its construction. is paper describes te one possible way to improve cooling capacity, CO and energy efficiency of R-134a A/C system of a medium size car. ree different experiments/tests are conducted under steady state conditions in a system test benc calorimeter, one witout eat excanger (baseline) and oter two wit different eat excangers. e experimental results sow tat cooling capacity of car A/C system increases by 4.84% and 3.17%, CO increases by 11% and 7.18% and compressor input power is reduced by 6.05% and 4.18% wit te use of copper and aluminum IX, respectively. Keywords Calorimeter, car A/C system, cooling capacity, CO, internal eat excanger (IX), subcooling. 1. INRODUCION any tecnologies are being used for enancing automotive R-134a A/C system performance. e IX tecnology is probably te simple one, yet it as not being given importance for its use on production veicles. e IX transfers eat from te condenser outlet to te suction gas for waste refrigeration recovery. e increased subcooling before expansion reduces evaporator inlet entalpy and tus increases te specific cooling capacity. e increased supereating of gas before compression reduces suction vapor density and increases compressor inlet temperature. e important strategy to be adopted wile using IX tecnology is to maximize subcooling and minimize supereating. e balance is to be maintained between subcooling and supereating in-order to acieve te efficient performance of A/C system. Kim et al. [1] studied te effect of liquid line suction line eat excanger (LLSL-X) for residential eat pump wit R-22, R-134a, R32/134a, R-407C and R-410 as a refrigerant. owever, LLSL-X is not used for car A/C system. Boewe et al. [2] used tube in tube type suction line eat excanger wit different tube lengts in transcritical R-744 mobile A/C system. All commercially available components are used but results are taken wit different compressors wit a maximum rpm of Bullard et al. [3] presented te results of *Department of ecanical Engineering, odern College of Engineering, Sivajinagar, une, aarastra, India. # Department of ecanical Engineering, Government College of Engineering, une, India. & Ber India Limited, une, India. 1 Corresponding autor; el: , Fax: modern_desai@yaoo.co.in. experimental runs of a prototype of R-744 refrigeration system meant for a compact car. ey used LLSL-X but its effects are not discussed in teir paper. Klein et al. [4] identified new dimensionless parameter attributable to LLSL-X. ey assumed te pressure drop in LLSL-X to be negligible. Also te test conditions are not well defined. Brown and Domanski [5] used LLSL-X in a semi-teoretical simulation model for a transcritical CO 2 mobile A/C System. Brown et al. [6] carried out comparative analysis of an automotive A/C system operating wit CO 2 and R-134a, using IX. e paper discussed only te simulation results. ey did not consider separately te effect of IX. arcus et al. [7] performed experiments wit Fixed Orifice ube (FO) and termostatic expansion valve (XV). It is concluded tat FO is more beneficial and IX elped to improve te efficiency of R-134a A/C system. ey do not mention te type of IX used. Zang et al. [8] tested te LLSL-X on a production veicle wit R-134a A/C system. ey concluded tat A/C systems wit LLSL-X ave benefits viz. low compressor discarge pressure, better performance and tere was no wet compression. Also te test conditions are not well defined. Kim et al. [9] experimental performance caracteristics of zoetrope are compared wit R-12, R-134a, R-22 and R-290 at ig temperature eating and cooling conditions including tose using liquid-line/suction-line eat excanger. It is concluded tat IX increased te performance of eat pump, owever it is not used for automotive A/C system. cenaney et al. [10] presented experimental analysis of te performance of a prototype A/C system based on transcritical operation wit R-744 as a refrigerant. IX was included in A/C system but its effects are not discussed. is paper presents te effect of IX on cooling capacity, power consumption and coefficient of

2 156 performance (CO) of medium size car A/C system. e wind tunnel results under various operating conditions of veicle are used as a support or real-world data to design te IX. wo tube-in tube type internal eat excangers of unequal lengts but of different materials are designed, fabricated and are tested under steady state conditions on a system test benc calorimeter. Keeping same, all te A/C components and te connecting tubes, of actual R-134a A/C system of a medium size car, experiments are performed wit two different IX and one witout IX (base line), under steady state conditions. e IX(s) are of tube in tube type eat excanger, wit fins on external surface of inner tube. e cold fluid (i.e. vapour refrigerant at outlet of evaporator-lower side) flows in te inner tube and ot fluid (i.e. liquid refrigerant at outlet from condenseriger side) between te annulus of inner and outer tube. e design is very compact and weigts are very low for bot te IXs. e sizes i.e. lengts and outer diameters are so selected tat te IX can be easily accommodated in te space available in car bonnet. Suc a comparative study of car A/C system comprising of compact IX A. D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) made up of copper and aluminum material is not available in te open literature. 2. DESCRIION OF E EXERIENAL ES BENC CALORIEER 2.1 Description e scematic of test benc calorimeter, experimental test setup and Dew oint Unit (DU) are sown in Figures 1, 2 and 3, respectively. e calorimeter and DU elps to maintain te correct temperature and umidity of air as per given test conditions. ese combined systems togeter can be used for testing complete VAC modules as well as for testing bare components, viz. evaporator, condenser, compressor etc. of automotive A/C system, working wit R-134a refrigerant. Wit tis test benc, a real life mounting of a veicle refrigerant circuit can be realized and ence it is utilized for testing complete automotive VAC system under real veicle conditions. e experimental test set up indicates various A/C system components, its tubings, location of IX and sensors utilized during experimentation. DU B B B B Air Drying V V V V F F F REURN REURN AIR AIR Camber-2 REAR VAC FRON VAC Camber- 1 CONDENSER ermo acoustic insulated cabin B - Blower F - Flexible ose - eat Excanger otorised Valve DU - Dew oint Unit V - V Cones otion of Air Fig. 1. Scematic of test benc calorimeter.

3 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) Compressor Drive motor rpm and orque meter Air out Valve Condenser wit receiver dryer Air in Carging system Refrigerant cylinder Weiging macine Oil concentration measurement device Refrigerant flow meter artition emperature sensor ressure sensor Air out to grills Air in R Evaporator XV ermo acoustic insulated cabin IX Fig. 2. Scematic of experimental test setup. Spray Nozzle Conditioned air-out wit controlled dew point to test sample / calorimeter camber packed column pump Air-in from calorimeter camber water level meter drain water tank ab water refill Fig. 3. Dew oint Unit (DU) for umidity control.

4 158 e entire test benc calorimeter consists of te following sub systems/modules. 1. Closed air loops for supply of conditioned air to condenser and evaporator. 2. R-134a refrigerant circuit wit compressor drive, speed control device and torque meter. 3. rimary and secondary brine circuits of ciller units to acieve te desired temperatures of air. 4. DU for controlling umidity of inlet air to condenser and evaporator. 5. V-cones for accurate measurement of air flow rates. 6. Lubricating oil concentration measuring device. 7. Coriolis type flow meter for refrigerant mass flow measurement. 8. ower supply system for various drives (AC and DC bot). 9. Control panel and data acquisition system. 10. Condensate measurement system - to determine latent eat load of moist air. 2.2 Experimental Apparatus e double camber layout is as sown in Figure 1. e camber 1 is for testing condenser and compressor were as camber 2 is meant for testing rear and front evaporators of automotive A/C system. e components like radial blower wit speed control unit, DU, deumidification unit, ciller, various sensors for measurement of pressures, temperatures, umidity, R, torque, mass flow rate of refrigerant and data acquisition system etc. are located inside te cambers. e airflow rate measuring V-cones, wit gas tigt flap are installed on top of te cambers. e complete system including air measuring sections are A. D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) covered wit noise and termal insulation. e camber / calorimeter is connected to te building ventilation system so tat te eat load of te camber / calorimeter can be dissipated to te atmospere. e water-cooled condenser of te cooling unit i.e. primary brine circuit is equipped wit a flow control valve, wic pumps te water into buffer tank from were te cold water is supplied to secondary circuiteat excangers. e eat excangers in DU and deumidifier receive te water (ot/cold) from te secondary circuit, for controlling umidity in te test camber. e refrigerant leak detection and recarging system consisting a vacuum pump, nitrogen cylinder, refrigerant carging and recovery unit, along wit lubricating unit and electronic weiging macine are separately available wit necessary oses and connections. Figure 4 (a, b) and Figure 5 (a, b) sow te inlet and outlet air temperature mappings of evaporator and condenser, respectively. Inlet air temperatures are measured by four numbers of -100 sensors and out let air temperatures by 16 numbers of K-type termocouples in case of an evaporator and condenser, respectively. Four numbers and one number of umidity sensor(s) are used for measurement of umidity of inlet air at evaporator and condenser, respectively. e average of tese values is considered for calculations. ermocouples and pressure transducers are mounted at various locations as sown in Figure 2 for te measurement of refrigerant temperature and pressure. All te sensors used for te temperature, pressure, torque, R and umidity measurement are calibrated prior to teir use. (a) /2 (b) /2 /2 W/2 W w/2 w w W w w w/2 Fig. 4. (a) and (b) Evaporator inlet and outlet air temperature mappings.

5 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) (a) w/2 (b) w W W w W/2 w w/2 /2 /2 /2 Fig. 5. (a) and (b) Condenser inlet and outlet air temperature mappings. 2.3 est conditions anufacturers generally ave teir own test conditions rater tan adopting an industry wide standard. is is done in order to be able to compare most recent test data wit te istorical data from previous testing. able 1 sows te typical test conditions used during experiments and teir significance. e airflow rates and te compressor rpm are selected, corresponding to blower knob position and veicle speed, respectively. e various tests conditions are for dry, umid, moderate and ig ambient conditions. e details of various test components utilized in tese tests are given in able 2. Experimental procedure and measurements All te actual components of A/C system of a medium size car are connected as sown in Figure 2. e carge determination test as described below is conducted to determine optimum carge quantity required for effective operation of A/C system. is will ensure proper working of A/C system wile driving at city and igway traffic conditions and varying ambient. 1. e A/C system is initially filled wit nitrogen gas at a pressure of 5 to 5.5bar and tis pressure is maintained for 30 minutes. us te system is assured for no leakages. 2. e A/C system is evacuated by nitrogen removal. 3. roug te refrigerant carging unit, to start wit, feed te A/C system wit a refrigerant carge of 350g. is carge quantity is approximately alf of actual carge and it is selected based on past experience and istorical data. 4. e system is allowed to stabilize for 10 minutes after eac addition of carge between 25g - 50g, till desired values of subcooling and supereating are reaced. In te present study supereating of refrigerant after evaporator between 5-12K and subcooling of refrigerant after condenser up to 10 K are considered for carge optimization. 5. us correct carge is determined as per above procedure for baseline and two IX tests (copper and aluminum IX) under consideration. 6. As per te tests conditions mentioned in able 1 experiments are conducted. e operating parameters namely air flow rates, air temperatures at inlet to condenser and evaporator are varied troug ID controller. e air flow rates over condenser are so selected to simulate te condition owing to actual veicle speed. In te present study R of air at evaporator inlet is also varied from dry ambient (R< 10%) to umid ambient of 50% R. e compressor rpm is varied from 600 rpm to a maximum value of 4000 rpm corresponding to idle and maximum speed (120 km/) of a veicle. 7. For eac of te test condition te readings are recorded after te system gets stabilized. e pressures, temperatures, umidity and mass flow rates of air and refrigerant are recorded by data logging system at various locations as sown in Figures 1 and e mass flow rate of air over evaporator and condenser are measured using V-cones wic are mounted on respective air inlet pipes. 9. esting is done for umid, dry, moderate and ig ambient conditions. e test conditions selected are severe as well as mild in nature corresponding to igway and city drive cycles. 10. e oil concentration in te refrigerant is also recorded during te test and it is found to be maximum of 5.02%, wic is below te tolerable limit [17].e accuracies of measured parameters are given in able e compressor input power is measured using te torque meter and its R. 12. ree tests/experiments are performed under steady state conditions one baseline (witout IX) and one eac wit copper and aluminum IX. All te necessary observations and readings are recorded.

6 160 A. D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) able 1. est conditions. Condenser Evaporator Compressor Significance of test est Condition No. emperature of air at inlet Air flow rate at inlet Air flow Velocity Air flow Rate at inlet emperature of air at inlet R of air at inlet R Blower knob position, veicle speed, ambient conditions ºC kg/min m/s kg/min ºC % rev/min Witin 5 minutes and cool downstabilized <10 (dry) 1000 o ceck te ot gas temperature for <10 (dry) 2500 different compressor R and at ig load condition <10 (dry) <10 (dry) t speed, 60 km/, ig ambient rd speed, veicle idle speed rd speed, 80 km/, low and umid ambient nd speed, 60 km/, low and umid ambient <20 (dry) nd speed, 60 km/, low ambient <20 (dry) rd speed, idle, low and dry ambient <20 (dry) 600 2nd speed, veicle idle, speed low and dry ambient. *Note: ese test condition are same for baseline (w/o IX), copper and aluminum IX tests.

7 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) able 2. Details of test components. Sr. Name of te Component Description 1. Compressor SE BX-11 reciprocating type 2. Compressor clutc 3. Condenser (W* * D) micro cannel brazed aluminum 4 pass Displacement cc, ax R = 9000, Weigt = 2.3 kg Lubricating oil grade and quantity ND8 140 cc compressor pulley diameter = 131 mm 7 grove, pulley ratio=1.16, stroke lengt = mm Rating 12 V, Engagement voltage 8 V, Current 3 to 3.4 A, ulley Dia 131 mm ulley ype V 7, Static friction torque 34 N-m Widt (mm) eigt (mm) Dept (mm) Flow pat Frontal area (m 2 ) ass (kg) Evaporator (W* * D) micro cannel brazed aluminum 4 pass XV (ermostatic Expansion valve) C3 Carge and 1.9 bar setting 6. Internal eat excanger (IX) Co axial tube in tube type, Counter flow, wit fins on external surface of inner tube. 6.1 aterial:- copper, externally finned inner tube 6.2 aterial:- aluminium, externally finned inner tube 7. R-134a Carge quantity * Lengt (mm) Outside Diameter (mm) ass (g) *Base line = 550 g *wit copper IX = 655 g *wit aluminum IX = 620 g Connecting tube dimensions (mm) Lengt of connecting tubes (mm) Outer diameter ickness copper IX aluminum IX Base line Suction line Liquid line Discarge line *Note: All te A/C components of a veicle are connected using actual piping and troug calorimetric carge determination tests for base line, copper and aluminum IX, te refrigerant optimum quantities are decided.

8 162 A. D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) able 3. Accuracy of measured parameters. ressure K type termocouple -100 sensor Rotational Speed (R) umidity Flow measurement % of oil concentration Weiging scale orque ig and Low ±1% (+2 a) i) Air: +1K ii) Refrigerant: +0.1K ±0.5 K +1% ±0.2 K of dew points in range 10 0 C to 30 0 C, For>30 0 Cdew point ±0.5K i) Air: ± 1% of measured value ii) Refrigerant: ±0.05% of full flow of measured value % g + 0.2% of measured value Fig. 6. oto of location of IX under test.

9 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) RESULS AND DISCUSSION e experimental data is processed so tat te system performance can be evaluated for different operating / test conditions mentioned in able 1, Figures 7, 8 and 9 sows te comparison of cooling capacity, CO and power input to compressor of AC system wit and witout IX at various test conditions and compressor speeds. ese graps / figures are plotted by using te experimental data collected / recorded during tese tests, for all te tree tests viz. base line, wit copper IX and aluminum IX. inimum and maximum power consumption of compressor of A/C system of a medium size car is also determined corresponding to idle and maximum engine rpm. e results of tese tests indicate significant influence of IX on te performance of A/C system of a car. e minimum speed of compressor corresponds to idle condition and maximum speed to 120 km/ of actual veicle speed. Figure 7 sows te comparison of cooling capacity of te A/C system for above named tree tests, wit te variation of compressor speed, wic is according to engine/veicle speed variation. e cooling capacity of te A/C system is iger for te compressor speed of 2500 rpm wit IX made up of copper in comparison wit base line system and te A/C system wit aluminum IX. e same trend is observed at all te oter compressor speeds. ere is a better eat excange rate, between te liquid refrigerant and vapor refrigerant in IX due to ig termal conductivity of copper metal. is results in te reduction of supereat of suction gas and improves subcooling of liquid refrigerant before it enters into te expansion device. e average subcooling is found to be K wit copper IX and K wit aluminum IX and is witin acceptable limits. e cooling capacity of te system is minimum for te compressor speed of 600 rpm. e mass flow rate of refrigerant varies according to compressor speed, terefore, low speed leads to lower cooling capacity of te A/C system. Figure 8 sows te comparison of CO of te A/C system for baseline and IX tests, wit te variation of 163 compressor speed wic in turn varies according to te engine /veicle speed. e CO is te ratio of cooling capacity to te input power of te compressor. is ratio is maximum at a compressor speed of 900 rpm, because of te fact tat power consumption at low rpm is less. owever te test conditions corresponding to compressor rpm of 600 are different tan at 900 rpm. ence te cooling effect and power consumptions are different at tese compressor speeds resulting in to variation in CO. Figure 9 sows te comparison of power input to te compressor of A/C system for baseline and IX tests, wit te variation of its speed wic varies according to te engine speed. e input power to te compressor is a function of refrigerant flow and its speed. e mass flow rate of refrigerant is minimum corresponding to its minimum speed. Furter following points are observed. 1. e average refrigerant pressure drop in copper IX is also very low of te order of 3.63 ka on iger side and 2.45 ka for low side. For aluminum IX te pressure drop is 4.09 ka and 1.36 ka on iger side and low side, respectively. 2. e refrigerant supereating at compressor inlet is observed to be K and K for copper and aluminum IX, respectively, wic is also witin tolerable limits and practice followed in industry. 3. ere is significant influence of IX on R-134a A/C system. It is observed tat cooling capacity and CO increases and tere is noticeable reduction in power input to te compressor. 4. e oil concentration in refrigerant, for base line, copper and aluminum IX tests, is also measured and is observed to be 5.02%, 3.93% and 4.65%, respectively wic is well witin te prescribed value. Fig. 7. Comparison of cooling capacity baseline, wit copper IX and aluminium IX.

10 164 A. D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) Fig. 8. Comparison of CO baseline, wit copper IX and aluminium IX. Fig. 9. Comparison of ower input to compressor- baseline, copper IX and aluminium IX. 4. CONCLUSION e experiments performed on system test benc calorimeter and its results ave proved tat IX improved te efficiency of R 134a A/C system of a medium size car noticeably. e size and weigt of IX developed in tis study is almost four times less as compared to te IX sizes of previous studies. 1. e overall improvement in cooling capacity of A/C system wit copper and aluminum IX is 4.84% and 3.17%, respectively. 2. e CO as increased by 11% and 7.18% in case of copper and aluminum IX, respectively. 3. e average compressor input power is reduced by 6.05% and 4.18% in case of copper and aluminum IX, respectively. 4. e refrigerant pressure drop in IX on iger side and lower side are very low as compared to te values. 5. e average refrigerant temperatures at compressor outlet are C, C and C for base line, copper and aluminum IX, respectively. 6. inimum power consumption by compressor at 600 rpm corresponding to a veicle/engine idle condition is found to be 0.54 kw for baseline, 0.52 kw eac for copper and aluminum IX. Similarly maximum power consumption by compressor at 4000 rpm corresponding to a veicle speed of 120 km/ is found to be 4.02 kw for baseline, 3.69 kw for copper and 3.91 kw for aluminum IX. REFERENCES [1] Kim,.-., Domanski,.A., Didion, D.A., erformance of R-22 alternative refrigerants in a system wit cross-flow and counter-flow eat excangers. National Institute of Standards and ecnology, Report No NISIR 5945: [2] Boewe, D., Yin, J., ark, Y.C., Bullard, C.W., and rnjak,.s., e role of suction line eat excanger in transcritical R744 mobile A/C System. Society of Automotive Engineers ecnical SAE: [3] Bullard, C.W., Yin J.., and rnjak,.s., ranscritical CO 2 mobile eat pump and A/C

11 A.D. Desai, S.N. Sapali and G.V. artasarati / International Energy Journal 12 (2011) system- experimental and model results. Veicle ermal anagement Systems London: [4] Klein, S.A., Reindl, D.. and Brownell, K., Refrigeration system performance using liquidsuction eat excangers. International Journal of Refrigeration 23(8): [5] Brown, J.S. and.a. Domanski, Semiteoretical simulation model for a transcritical carbon dioxide mobile A/C system. Society of Automotive Engineers World Congress ecnical aper Series: :1-11. [6] Brown, S., Yana-otta, S.F., and Domanski,.A., Comparative analysis of an automotive air conditioning systems operating wit CO 2 and R134a. International Journal of Refrigeration 25: [7] reissner,., Zang, C., Dickson,., R134a Suction line eat excangers in different Configuration of automotive air-conditioning systems. Society of Automotive Engineers ecnical aper Series [8] Zang, C.A., Graam, B.L., and Dickson,.R., ow to improve veicle R134a A/C system performance wit a liquid line suction line eat excanger (IX). Society of Automotive Engineers ecnical aper Series [9] Kim,.S., ulroy, W.J., and Didion, D.A., erformance evaluation of two Azeotropic refrigerant mixtures of FC-134a wit R-290 (propane) and R-600a (isobutane). ransactions of te ASE June 148(116). 165 [10] cenaney R. and. rnjak, Clutc cycling mode of compressor capacity control of transcritical R744 systems compared to R134a systems. Society of Automotive Engineers [11] Kern D.Q., rocess eat transfer. 21 st reprint ata c Graw ill publication, India. [12] atur,.l. and F.S. eta, Refrigerant and sycometric properties. ables and Carts, 1 st Edition, 6 t Reprint. Jain Broters ublication, New Deli, India. [13] Society of Automotive Engineers International Standards andbook (SAE J6368) Surface veicle recommended practice, pp [14] Society of Automotive Engineers International Standards andbook (SAE J6368) otor veicle eater est rocedure SAE Recommended ractices, pp 1-6. [15] ASRAE andbook, VAC applications. Capter 9: Atlanta USA Inc. [16] Kuppan,., eat Excanger Design andbook, 1 st Edition. aylor and Francis Group, NY, London, pp [17] Wandell, E., Dunn, W., iller, N., and Newell,., Conditions at Limit Oil Circulation in a obile Air-Conditioning System," SAE ecnical aper [18] Japanese Industrial Standard anual, Automobile air conditioning - testing metod JIS D1618, pp 1-11.

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